Devices for the automated release of liquid medicaments can be used with patients who have a continuous and/or, in the course of the day, a varying need of a medicine that can be administered by subcutaneous infusion. Specific applications include, for example, certain pain therapies and the treatment of diabetes. In such cases, computer controlled infusion pump devices may be used, which can be carried by the patient on the body, and which contain a certain amount of liquid medicament in a medicine reservoir. The medicine reservoir can comprise enough medicine sufficient for one or several days. Furthermore, the liquid medicament can be supplied to the patient's body from the medicine reservoir through an infusion cannula or an injection needle.
In self-administration of medicaments, such as, for example, insulin, the patients using the medicament in question and administering it themselves by means of an infusion pump device may seek convenience and discretion. As a consequence, the acceptable dimensions of such infusion pump devices may be limited in order not be evident through clothing and to be carried in a comfortable manner. In one type of infusion pump device, the liquid medicament may be obtained by a downstream pump from a flexible container. Flexible containers can comprise a smaller volume surplus of the container in relation to its content, which can reduce the manufacture costs and the achievable overall dimensions of an infusion pump device with such a flexible container.
However, infusion pump devices can include air bubbles in the fluidic system, particularly in the pump system, and in other components, such as the container. If air bubbles remain in the fluidic system, they may be administered instead of the liquid medicament. Also, due to the high compressibility of gases in relation to liquids such as water, the air can reduce the stiffness of the fluidic system, which may limit the potential detection of blockages or occlusions in the fluidic system when monitoring the fluidic pressure. Furthermore, fluidic systems can include dead volume which may not be emptied or drained completely. Thus, since a certain percentage of the liquid medicament inevitably remains in the fluid system and has to be disposed, the dead volume can increase the costs per dose and thus of the overall therapy costs.
Micro-fluidic chambers can be used, for example, as sensor chambers in pressure sensors for fluidic systems. Such pressure sensors can comprise a chamber filled with liquid that is fluidly connected to the fluidic system. The chamber can be covered by a flexible, resilient membrane, such that a pressure difference between the fluidic pressure inside the sensor chamber and the outside (atmospheric) pressure will temporarily deform the membrane. The resulting deflection of the membrane can then be measured to determine the internal pressure of the fluidic system.
One possible approach to measure the deformation of the membrane includes the optical detection of a light beam reflected by the membrane. Another possible approach can include capacitive sensing, in which the flexible, resilient membrane of the chamber acts as a capacitor electrode. When the membrane is deformed, the capacitance between the membrane capacitor electrode and a second capacitor electrode changes and is measured to determine the pressure difference acting on the membrane. Yet another possible approach to measure the deformation of the membrane is the use of strain gauges mounted to the membrane. In the context of liquid medicament administration via an infusion pump device, these exemplary pressure sensors, as well as alternative apparatuses and methods, may be used for controlling the dosing, monitoring the correct operation of the system, and detecting faults and hazards, such as occluded infusion lines or cannulae, empty containers, or malfunctioning pump systems. However, air bubbles in the in the micro-fluidic sensor chamber can reduce the stiffness of the fluidic system, and thus delay the response of the sensor to pressure changes in the fluidic system. The resulting irreproducible measurement errors may reduce the dosing accuracy of an infusion pump device, and increase the response time to an occlusion event.
Micro-fluidic chambers may also be employed as degassing devices for fluidic systems, particularly infusion pump devices, in which a liquid filled chamber may be covered by a gas-permeable membrane. Subject to the condition that there is a positive difference between the partial pressure of the gas present in the fluidic system and the pressure on the opposite side of the permeable membrane, gas, as bubbles or solved in the liquid, can leave the fluidic system by permeating through the membrane. In such uses, the properties of the micro-fluidic chamber and the performance of devices using such chambers may be independent on the orientation of the micro-fluidic chamber with respect to the gravity field, since the orientation of the device during application is undefined and may constantly change
Thus, to limit or avoid air bubbles in the micro-fluidic chamber when the fluidic system is filled the first time, the so called priming of the system, the chamber may be filled in a controlled manner. However, the micro-fluidic chamber may comprise an uncontrolled orientation during this first filling procedure since the gravitation field leads to buoyancy forces that act on the air bubbles. Depending on the orientation and the design of the micro-fluidic chamber, air bubbles may be caught in certain areas of the chamber.
Accordingly, a need exists for alternative micro-fluidic chambers for use in liquid medicament delivery systems.
For the present specification the meaning of the term “air” shall not only include air as such, but any gas or composition of gases that may be present in a fluidic system, particularly pure nitrogen or other protective gases.